The present invention relates to a double chainstitch sewing machine for forming stitches for applying a cover thread at the lower side or upper and lower sides of a workpiece.
FIG. 11 shows a double chainstitch sewing machine for forming stitches related to stitch type number 407 and others designated in the United States Federal Standards No. 751a.
In this sewing machine, the needle thread is first passed from a thread tension device 117 into a thread eye of a first thread take-up 116 through a fixed thread guide 114. In succession, the needle thread is passed into a thread eye of a movable thread guide 115 through a U-shaped second thread take-up 118, and is passed into an eyelet of a needle holder 120 at the lower end of a needle bar 112 and an eyelet of a needle 119.
When forming stitches for applying a cover thread at the upper and lower sides of a workpiece by this double chainstitch sewing machine, an upper cover thread mechanism disclosed in Japanese Utility Model 63-26144 is disposed beneath a sewing machine head 111a. The upper cover thread is supplied into the upper cover thread mechanism by way of a thread take-up for upper cover thread (not shown) provided in the first thread take-up 116 from the thread tension device 117.
The movable thread guide 115 is affixed to the upper end of the needle bar 112, and moves up and down together with the needle bar. The first thread take-up 116 is affixed to an oscillating shaft 113, and oscillates about the shaft. All these members move up and down or oscillate outside of the sewing machine arm 111 and are hence dangerous. Accordingly, to protect the operator from danger, a guard is required, but such guard makes it difficult to pass the thread. If the guard is designed to be opened and closed for the ease of passing of thread, it leads to a cost increase.
Further, in this sewing machine, there is a probability of oil leak from the support parts of the needle bar projecting from the top of the sewing machine arm, and the oscillating shaft projecting to the front side of the sewing machine arm.
In such double chainstitch sewing machine, the needle thread from the thread tension device to the workpiece runs for a long thread pathway extending from the thread tension device to the workpiece by way of the fixed thread guide, first thread take-up, second thread take-up and movable thread guide. Accordingly, it is likely to have effects of stretchable characteristic of thread, and it is hard to obtain an optimum thread take-up amount.
Especially in largely stretchable thread such as woolly thread, the movable thread guide, first thread take-up and second thread take-up act more to stretch thread than to take up thread, so that the take-up action is unstable. It is hard to adjust by the first and second thread take-up amounts and is hence difficult to obtain a double chainstitch of a desired touch. Still more, since the upper cover thread is taken up at the same timing as the needle thread, it is hard to obtain a desired covering chainstitch.
It is hence an object of the present invention to eliminate the difficulty in threading without substantially increasing the cost, by eliminating movable thread take-up members on the upper side and front side of the sewing machine arm, and installing substituent movable thread guide and first and second thread take-ups centrally at the lower end of the needle bar or jaw of the sewing machine arm so as to decrease the dangerous positions for the operator. It is other object of the present invention to avoid the probability of oil leak from the support parts of the needle bar projecting from the top of the sewing machine arm, and the oscillating shaft projecting to the front side of the sewing machine arm.
It is a further object of the present invention to present a double chainstitch sewing machine capable of obtaining a desired stitch tension easily by shortening the thread pathway length from the workpiece to the thread tension device and decreasing effects of thread stretchable characteristic on take-up of needle thread, and a double chainstitch sewing machine related to a flat seam for taking up upper cover thread at optimum timing by installing a thread take-up for upper cover thread independently of a thread take-up for the needle thread.
In a first aspect of the double chainstitch sewing machine according to the present invention, a movable thread guide for guiding the needle thread is fixed to the lower end of the needle bar. A fixed thread guide is fixed to the jaw of the sewing machine arm. A thread take-up cam is also fixed to the jaw of the sewing machine arm, and the cam section of the thread take-up cam extends in the vertical direction by intersecting with the needle thread pathway between the fixed thread guide and the movable thread guide. The needle thread from the fixed thread guide to the movable thread guide is oscillated up and down from the fixed thread guide by the movable thread guide moving up and down together with the needle bar, and is supplied into the cam section of the thread take-up cam. Thus, by interaction of the movable thread guide and the cam section of the thread take-up cam, the needle thread is taken up from the thread tension device to the needle.
In a second aspect of the double chainstitch sewing machine according to the present invention, a movable thread guide for guiding the needle thread is fixed to the lower end of the needle bar, and a fixed thread guide having mutually opposite right and left thread eyes is fixed to the jaw of the sewing machine arm. A thread take-up cam is also fixed to the lower end of the needle bar, and the cam section of the thread take-up cam is disposed between the thread eyes of the fixed thread guide. The needle thread from the fixed thread guide to the movable thread guide is oscillated up and down from the fixed thread guide by the movable thread guide moving up and down together with the needle bar, and the needle thread between the thread eyes of the fixed thread guide is bent by the vertical motion of the cam section of said thread take-up. Thus, by interaction of the movable thread guide and the thread take-up cam, the needle thread is taken up from the thread tension device to the needle.
According to these aspects of the present invention, since the thread take-up oscillating vertically at the front side of the sewing machine arm and the movable thread guide moving vertically as being affixed to the upper end of the needle bar are eliminated, the operator is liberated from the danger during operation of the sewing machine at the front side and upper side of the sewing machine arm. At the same time, the support parts of the needle bar projecting from the top of the sewing machine arm, and the oscillating shaft projecting to the front side of the sewing machine arm in the conventional sewing machine can be eliminated, and probability of oil leak is avoidable. Further, the movable thread guide of the thread take-up mechanism is attached to the lower end of the needle bar, the fixed thread guide is fixed and installed at the jaw of the sewing machine arm, and the thread take-up cam is attached to the lower end of the needle bar or fixed and installed at the jaw of the sewing machine arm, so that the thread take-up action of the needle thread takes place near the needle, and the thread pathway length from the workpiece to the thread tension device can be shortened, and the thread take-up action of the needle thread is done without substantially having effects of the stretchable characteristic of the thread.
In a third aspect, relating to a double chainstitch sewing machine having a plurality of needles, two or more thread eyes are provided in the movable thread guide, and are disposed obliquely to the motion direction of needle bar.
In a fourth aspect, relating to a double chainstitch sewing machine having a plurality of needles, two or more thread eyes are provided in the movable thread guide, the fixed thread guide is composed of a plurality of thread guide members, and each thread guide member can adjust the guiding position of the needle thread individually.
In the double chainstitch sewing machine having a plurality of needles, the eye of each needle is different in height in order to match the timing with the eyelet of the looper, and the needles are arranged obliquely. In the present invention, since the thread eyes of the movable thread guide are arranged obliquely, or the thread guide members of the fixed thread guide can be adjusted individually, the thread take-up amount necessary for each needle thread can be assured.
In a fifth aspect of the double chainstitch sewing machine according to the present invention, the thread tension device for adjusting the tension of the upper cover thread is provided at the front side of the sewing machine arm, and an upper cover thread mechanism having a spreader for swinging the upper cover thread laterally to be engaged with the needle thread is provided at the jaw of the sewing machine arm, said upper cover thread mechanism is comprised a fixed thread guide for guiding the upper cover thread and a thread swing guide. The thread swing guide has a thread eye for leading the upper cover thread from the fixed thread guide to a thread lead tool, and a slot for leading the upper cover thread from the thread lead tool to the spreader. The spreader includes a thread take-up tool for taking up the upper cover thread by engaging with the upper cover thread from the fixed thread guide to the thread swing guide.
According to the present-invention, since the thread take-up tool for the upper cover thread is attached to the spreader, the motion of the thread take-up tool is synchronized with the motion of the spreader, and the upper cover thread is taken up independently of the thread take-up tool of the needle thread.
In a sixth aspect, since the upper end of the needle bar is positioned within the sewing machine frame and the length of the needle bar is shortened, it is able to reduce the weight of the needle bar and to increase the sewing machine speed.
In a seventh aspect, the needle bar drive mechanism comprises an oscillating shaft crossing orthogonally with the upper shaft and oscillating in cooperation with the rotation of the upper shaft, and a lever fixed to the oscillating shaft for driving the needle bar as being coupled to the upper end of the needle bar.
Other features and effects of the present invention will be more clearly understood in the following detailed description of the embodiments by those skilled in the art. It must be, however, noted that the technical scope of the present invention is not limited to the embodiments and the accompanying drawings alone.